Wide operational windows of edge-localized mode suppression by resonant magnetic perturbations in the DIII-D tokamak

TL;DR

This study demonstrates that by adjusting plasma density and RMP parameters, wide operational windows for ELM suppression can be achieved in the DIII-D tokamak, which is crucial for future reactor safety and flexibility.

Contribution

The paper reveals how plasma density influences the width of ELM suppression windows and predicts conditions for achieving broader suppression ranges using higher mode number RMPs.

Findings

Wider q95 ELM suppression windows occur at lower plasma densities.

Nonlinear simulations match experimental q95 windows and density dependence.

Higher mode number RMPs can extend ELM suppression to higher pedestal pressures.

Abstract

Edge-Localized-Mode (ELM) suppression by resonant magnetic perturbations (RMPs) generally occurs over very narrow ranges of the plasma current (or magnetic safety factor q95) in the DIII-D tokamak. However, wide q95 ranges of ELM suppression are needed for the safety and operational flexibility of ITER and future reactors. In DIII-D ITER Similar Shape (ISS) plasmas with n=3 RMPs, the range of q95 for ELM suppression is found to increase with decreasing electron density. Nonlinear two-fluid MHD simulations reproduce the observed q95 windows of ELM suppression and the dependence on plasma density, based on the conditions for resonant field penetration at the top of the pedestal. When the RMP amplitude is close to the threshold for resonant field penetration, only narrow isolated magnetic islands form near the top of the pedestal, leading to narrow q95 windows of ELM suppression. However, as the threshold for field penetration decreases with decreasing density, resonant field penetration can take place over a wider range of q95. For sufficiently low density (penetration threshold) multiple magnetic islands form near the top of the pedestal giving rise to continuous q95 windows of ELM suppression. The model predicts that wide q95 windows of ELM suppression can be achieved at substantially higher pedestal pressure in DIII-D by shifting to higher toroidal mode number (n=4) RMPs.